The present invention relates to the field of non-contact fluid marking devices commonly known as "ink-jet" or "fluid-jet" devices. More particularly, the present invention relates to a fluid-jet distribution bar and to methods for forming and assembling a fluid distribution bar used in such non-contact fluid marking devices for flowing fluid through an orifice plat.
Fluid-jet devices in and of themselves are well known. Typically, prior art fluid-jet devices provide a linear array of fluid-jet orifices formed in an orifice plate from which filaments of pressurized fluid (e.g., ink, dye, etc.) are caused to issue from a fluid supply channel. A controllable electrostatic charging electrode is disposed downstream of the orifice plate along the so-called "drop formation" zone. In accordance with well-known principles of electrostatic induction, the fluid filament is caused to assume an electrical potential opposite in polarity and related in magnitude to the electrical potential of its respective charging electrode. When a droplet of fluid separates from the filament, the induced electrostatic charge is then trapped on and in the droplet. Thus, subsequent passage of the charged droplet through an electrostatic field having the same polarity as the droplet charge will cause the droplet to be deflected away from a normal droplet path twoards a droplet catching structure. Uncharged droplets, on the other hand, proceed along a normal path and are eventually deposited upon a substrate.
It will be appreciated that the orifice plate has a linear array of very small orifices having diameters in the range, for example, of about 0.0013-0.01 inches. In fabricating fluid-jet devices of this general type, there is provided a fluid distribution bar having a plenum which supplies fluid to the orifice plate at uniform pressure and minimal turbulence. However, when the orifice array extends a substantial distance, for example 1.8 meters, and recognizing the extremely small orifice size, technical difficulties obtain in providing a uniform fluid supply for distribution through the orifices. For example, air bubbles in the fluid, when confronting the orifices of the orifice plate, have a tendency to prevent the fluid from flowing or distort the fluid flowing through the orifices. This results in a non-uniform flow curtain below the orifice plate, possible interference between adjacent flow streams issuing from the orifices, and possible canting of the flow streams from their desired direction perpendicular to the orifice plate.
Additionally, sagging in the middle of the distribution bar and, hence, the orifice plate, because of their relatively long lengths, must be avoided. Thus, structural problems are a consideration in the design of a distribution bar.
The present invention is directed to a fluid distribution bar and methods of assembly and operation of a fluid distribution bar for use in a fluid-jet printing apparatus. The present invention provides a fluid distribution bar having fluid distribution channels in communication with the orifice plate constructed such that uniform pressure and minimum eddies and turbulence occur in the fluid, the fluid being provided substantially free of air bubbles. To accomplish this, preferably three superposed distribution channels are provided along the bar. Each channel has a separate inlet and outlet. The lowermost and intermediate channels have upper surfaces which are shaped to direct gas, e.g., air bubbles, rising in the fluid in the channels to high points or apices located at longitudinally spaced positions along the channels. These high points are in communication through ports with the next higher channel whereby the air bubbles flow from the lower channel(s) into the higher channel(s). Additionally, the upper surfaces of the intermediate and lower channels are shaped and the ports located to minimize movement of the fluid and, hence, minimize eddy currents and turbulence. Additionally, those ports serve as fluid inlet ports for the lower channel which feeds fluid to the orifice plate for flow through the orifices. Baffles are provided in the form of bosses in the lower channel to avoid direct impingement of the fluid entering the lower chamber through the ports on the orifice plate. The channels are also formed to have smooth continuous uninterrupted surfaces throughout their lengths whereby corners, sharp turns and the like in the channels are avoided, as well as the turbulence and eddy currents associated with such flow paths
Additionally, in view of the substantial length of the distribution bar, the need to form the channels as indicated above, and to avoid deflections caused by the weight of the bar, the bar is preferably formed of cast metal. Preferably, the bar is formed from identically cast half-sections of stainless steel. Each half-section has portions of a plurality of internal channels configured, when the bar sections are mated to provide a non-turbulent, substantially damped, flow to the orifice plate. The identically cast half-sections of stainless steel are preferably formed in a conventional casting mold, such as a sand mold. These two half-sections are then joined together along longitudinally extending side faces thereof, for example, by bolts.
A significant feature of the present invention resides in the ability to rapidly change the type or color of the fluid flowing through the channels and orifice plate without stopping fluid flow through the orifices. Shutdown of the flow through the orifices causes substantial problems, both in cleaning the channels and in starting the flow of fluid through the orifice plate. However, it is essential to ensure that the changeover from one fluid type or color to another is accomplished without leaving any residue of the first fluid in the distribution bar. The multiple channels permit such changeover without shutdown, without causing any change in the flow of the fluid filaments through the orifice plate (other than the transition from the first fluid to the second), and without any apparent change from normal operation during the changeover of fluids.
In normal operation, the inlet and outlet for the lower channel are closed, the outlet for the intermediate channel is closed, and a vacuum is applied to the upper channel. Thus, fluid is supplied through the inlet to the intermediate channel and gas is removed from the upper channel. In changeover, however, all three channels are opened at one end of the bar to serve as inlets for receiving the new fluid and all three channels are opened at the other end of the bar to serve as outlets for the old fluid and any mixture of the old and new fluids. Atmospheric or a slightly elevated pressure is maintained in the bar during changeover so that the fluid jets still run. Thus, there is horizontal flow across the bar as the fluid continues to issue through the orifices of the orifice plate. Changeover is in about 50 seconds with acid dyes for a bar about 1.8 meters long, much shorter than if only the middle level channel was used for changeover. Such quick changes can be of importance when using the fluid jet device to apply dyes to fabrics, since multiple color changes may be needed in a relatively short period of time. Thus, fluid of a different type or color may be introduced to one end of the bar into the multiple channels. As the new fluid enters, the old fluid is removed by continuing to issue through the orifices, as well as by flow through the channel outlets at the opposite end of the bar. A restriction is preferably located in the outlets to elevate the pressure in the bar during changeover in order to maintain sufficient pressure to continue the flow through the orifices. The new fluid simply replaces the old fluid as the latter runs out of the bar without the need for shutdown or first draining the old fluid before replacing it with the new fluid. Also, the continuous, smooth nature of the channels permits the new fluid essentially to flush the old fluid from the bar without leaving any residue.
Accordingly, in accordance with the present invention, apparatus is provided for supplying fluid to the orifice plate of a fluid-jet applicator comprising an elongated fluid distribution bar having a pair of elongated channels extending from adjacent one end of the bar to adjacent the opposite end of the bar, one of the channels being disposed above the other channel. Means are carried by the bar defining an inlet for supplying fluid to the channels. Means are additionally provided for defining an elongated slot for flowing the fluid outwardly of the other channel for flow through the orifice plate. Means are also provided defining at least one port providing communication between the channels and further means are provided for directing gases entrained in the fluid in the other channel to the port for flow through the one channel outwardly of the bar.
Preferably, the gas-directing means includes shaped upper surfaces in the other or lower channel which includes a plurality o f high points spaced longitudinally along the upper surface of such other channel coincident with a plurality of ports which are spaced longitudinally one from the other along the bar providing communication between the channels. Additionally, a third channel is disposed above the one or intermediate channel and has a plurality of ports spaced longitudinally therealong providing for communication between the third channel and the one channel, the ports being out of phase with the ports providing communication between the intermediate and lower channels.
In a preferred form of the present invention, the fluid distribution bar is formed of tow identically cast sections, each defining a portion of each channel, together with means for securing the cast sections one to the other to lie on opposite sides of the longitudinal centerline of the bar, with the cast channel portions in opposition one to the other.
In accordance with the present invention, there is also provided a method for forming a fluid distribution bar for use in flowing fluid to an orifice plate in a fluid-jet printing device wherein the bar has at least a pair of channels, one superposed over the other, including the steps of casting two identical elongated sections each defining portion of each channel, with each channel portion opening through a side face of the cast section, providing communication between the channels and securing the cast sections one to the other with the side faces abutting one another and the channel portions opening into one another to form the superposed channels.
In accordance with a further aspect of the present invention, there is provided a method of changing from one type of fluid to another in the fluid distribution bar of a fluid-jet printing device, the bar having at least a pair of channels, one superposed over the other, in communication with one another and an orifice plate comprising the steps of flowing a first fluid into the channels to form a fluid-jet curtain issuing from the orifices through the orifice plate, maintaining the fluid-jet curtain formed by the first fluid, while introducing into the channels a second fluid of a different type, and continuing to maintain the fluid-jet curtain as the second fluid displaces the first fluid in the channels of the distribution bar and in the formation of the fluid-jet curtain whereby the fluid forming the fluid-jet curtain changes from the first fluid to the second fluid.
In a still further aspect of the present invention, there is provided a method of operating the fluid distribution bar of a fluid-jet printing device, the bar having at least a pair of channels, one superposed over the other, in communication with one another and an orifice plate, comprising the steps of flowing a fluid into the channels to form a fluid-jet curtain issuing from the orifice through the orifice plate, applying a vacuum to the fluid in the distribution bar and flowing gases entrained in the fluid from the lower channel into the superposed channel for removal from the distribution bar.
Accordingly, it is a primary object of the present invention to provide a novel and improved fluid distribution bar for use in a fluid-jet device and methods for forming and using such fluid distribution bar for flowing fluid through an orifice plate in a manner enabling gas entrained in the fluid to be removed before it reaches the orifice plate, providing non-turbulent, damped flow of fluid to the orifice plate, and affording quick changeover of fluids from one to another.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings